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tipping points
Antarctic Tipping Point That Occurred 8,000 Years Ago 'Could Happen Again'
"We now have direct evidence that this ice sheet suffered rapid ice loss in the past," said a Cambridge researcher.
Feb 09, 2024
As European Union scientists confirmed that last month continued a worrying trend of historically high temperatures, U.K. researchers released a study Thursday warning how fossil fuel-driven global heating could lead to catastrophic and rapid ice loss in Antarctica not seen for thousands of years.
The study, published by researchers at the British Antarctic Survey (BAS) and the University of Cambridge in Nature Geoscience, relies on an ice core from the West Antarctic Ice Sheet that is over 2,100 feet long.
"We now have direct evidence that this ice sheet suffered rapid ice loss in the past," said senior author and Cambridge Earth sciences professor Eric Wolff in a statement. "This scenario isn't something that exists only in our model predictions and it could happen again if parts of this ice sheet become unstable."
"The very same processes we are seeing just beginning now, in areas like Thwaites Glacier, have played out before in similar areas of Antarctica and indeed, the pace of ice loss was equal to our worst fears about a runaway ice loss."
Study co-author and BAS researcher Isobel Rowell explained that "we wanted to know what happened to the West Antarctic Ice Sheet at the end of the Last Ice Age, when temperatures on Earth were rising, albeit at a slower rate than current anthropogenic warming."
"Using ice cores we can go back to that time and estimate the ice sheet's thickness and extent," she continued. The team measured stable water isotopes and the pressure of air bubbles in the core, and found that the ice sheet "shrank suddenly and dramatically" about 8,000 years ago.
"We already knew from models that the ice thinned around this time, but the date of this was uncertain," Rowell noted, referencing estimates of 5,000-12,000 years ago. "We now have a very precisely dated observation of that retreat that can be built into improved models."
The West Antarctic Ice Sheet is vulnerable because lots of it is on bedrock that's below sea level.\n\nIt looks like warm ocean water getting underneath triggered melting 8,000 years ago, before it stabilised at today's size.\n\nHuman-induced warming could restart the retreat.\n\n\ud83e\uddf53/3— (@)
Previous models also didn't indicate how quickly the retreat happened. However, the team's measurements showed that "once the ice thinned, it shrunk really fast," said Wolff.
"This was clearly a tipping point—a runaway process," he added. "It's now crucial to find out whether extra warmth could destabilize the ice and cause it to start retreating again."
University of Colorado Boulder glaciologist Ted Scambos was not involved with the study, but he called it "an excellent piece of detective work" and toldCNN that its takeaway message is "the amount of ice stored in Antarctica can change very quickly—at a pace that would be hard to deal with for many coastal cities."
CNN pointed out that the study contributes to mounting warnings from scientists about conditions in Antarctica:
For example, the Thwaites Glacier, also in West Antarctica, is melting rapidly. A 2022 study said the Thwaites—dubbed the Doomsday Glacier for the catastrophic impact its collapse would have on sea-level rise—was hanging on "by its fingernails" as the planet warms.
This new study adds to these concerns, Scambos said. "[It] shows that the very same processes we are seeing just beginning now, in areas like Thwaites Glacier, have played out before in similar areas of Antarctica and indeed, the pace of ice loss was equal to our worst fears about a runaway ice loss."
As Common Dreamsreported in October, a study published in Nature Climate Change found that the West Antarctic Ice Sheet—which contains enough ice to increase the global mean sea level by over 17 feet—faces an "unavoidable" increase in melting for the rest of this century.
"If we wanted to preserve it in its historical state, we would have needed action on climate change decades ago," lead author and BAS researcher Kaitlin Naughten said at the time—while also stressing that "we must not stop working to reduce our dependence on fossil fuels."
The release of that study preceded the 28th United Nations Climate Change Conference in Dubai. After COP28 ended in December with a final agreement that did not explicitly endorse a global phaseout of fossil fuels, scientists called it a "tragedy for the planet."
Despite the heat that the United Arab Emirates caught for having a fossil fuel CEO lead the latest summit, COP29 host Azerbaijan plans to have an oil executive head the next one, scheduled for November. Azerbaijan also plans to boost its gas production by a third during the next decade.
The COP29 host is far from alone. Global Witness revealed last month that the oil and gas companies that signed a decarbonization pact at last year's conference plan to burn through around 62% of the world's carbon budget by 2050—which sparked fresh demands for governments to stop caving to polluters and implement more ambitious climate policies.
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Scientists Say Risk of 5 Climate Tipping Points Means 'Business as Usual Is Now Over'
"Averting this crisis—and doing so equitably—must be the core goal of COP28 and ongoing global cooperation," one expert said.
Dec 06, 2023
An earlier version of this article said the sea levels could rise by 656 feet by 2100 if the Antarctic ice sheet started to melt. It has been corrected to reflect the fact that they would rise by 6.6 feet.
Current levels of global heating from the burning of fossil fuels and the destruction of nature risk triggering five tipping points that could throw Earth's systems further out of balance, with three more at risk of toppling in the next decade.
The Global Tipping Points Report, released Wednesday at the United Nations Climate Change Conference (COP28) in the United Arab Emirates, argues that policymakers have delayed climate action long enough that "linear incremental change" will no longer be enough to protect ecosystems and communities from the worst impacts of the climate crisis. However, world leaders can still choose to take advantage of positive tipping points to drive transformative change.
"The existence of tipping points means that 'business as usual' is now over," the report authors wrote. "Rapid changes to nature and society are occurring, and more are coming."
"Crossing these thresholds may trigger fundamental and sometimes abrupt changes that could irreversibly determine the fate of essential parts of our Earth system for the coming hundreds or thousands of years."
The report defines a "tipping point" as "occurring when change in part of a system becomes self-perpetuating beyond a threshold, leading to substantial, widespread, frequently abrupt and often irreversible impact." A group of more than 200 researchers assessed 26 different potential tipping points in Earth's systems that could be triggered by the climate crisis.
"Tipping points in the Earth system pose threats of a magnitude never faced by humanity," report leader Tim Lenton of Exeter's Global Systems Institute said in a statement. "They can trigger devastating domino effects, including the loss of whole ecosystems and capacity to grow staple crops, with societal impacts including mass displacement, political instability, and financial collapse."
Because current emissions trajectories put the world on track for 1.5°C of warming, this is likely to trigger five tipping points, the report authors found. Those tipping points are the melting of the Greenland and Antarctic ice sheets, the mass die-off of warm-water coral reefs, the thawing of Arctic permafrost, and the collapse of the North Atlantic Subpolar Gyre circulation.
The melting of just the Antarctic ice sheet, for example, could raise global sea levels by 6.6 feet by 2100, Carbon Brief reported, meaning 480 million people would face yearly coastal flooding. Three more tipping points could be triggered in the 2030s if temperatures rise past 1.5°C. These include the mass death of seagrass meadows, mangroves, and boreal forests, according to The Guardian.
"Crossing these thresholds may trigger fundamental and sometimes abrupt changes that could irreversibly determine the fate of essential parts of our Earth system for the coming hundreds or thousands of years," co-author Sina Loriani of the Potsdam Institute for Climate Impact Research told The Guardian.
Contributor Manjana Milkoreit of the University of Oslo said in a statement that "our global governance system is inadequate to deal with the coming threats and implement the solutions urgently required."
But that doesn't mean the report authors believe that hope is lost. Rather, they see it as a call to ambitious action at the current U.N. climate talks and beyond.
"Averting this crisis—and doing so equitably—must be the core goal of COP28 and ongoing global cooperation," Milkoreit said.
One way to do this is to take advantage of positive tipping points.
"Concerted actions can create the enabling conditions for triggering rapid and large-scale transformation," the report authors wrote. "Human history is flush with examples of abrupt social and technological change. Recent examples include the exponential increases in renewable electricity, the global reach of environmental justice movements, and the accelerating rollout of electric vehicles."
The report authors made six recommendations based on their findings:
- Immediately phasing out fossil fuels and emissions from land use changes like deforestation;
- Strengthening plans for adaptation and loss and damage in the face of inevitable tipping points;
- Taking tipping points into account in Paris agreement mechanisms like the global stocktake and national climate pledges;
- Collaborating to trigger positive tipping points;
- Organizing a global summit on tipping points; and
- Increasing research on tipping points, including through a special report by the Intergovernmental Panel on Climate Change.
"Now is the moment to unleash a cascade of positive tipping points to ensure a safe, just, and sustainable future for humanity," Lenton said.
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Study Warns Even With Emissions Cuts, West Antarctic Ice Sheet Melt 'Unavoidable'
"It looks like we've lost control of melting of the West Antarctic Ice Sheet," said one author. "The bright side is that by recognizing this situation in advance, the world will have more time to adapt to the sea-level rise that's coming."
Oct 23, 2023
Even if humanity dramatically reduces planet-heating pollution from fossil fuels, the West Antarctic Ice Sheet faces an "unavoidable" increase in melting for the rest of this century, according to a study published Monday in the journal Nature Climate Change.
The West Antarctic Ice Sheet is the continent's largest contributor to rising seas and contains enough ice to increase the global mean sea level by over 17 feet, the study explains. Enhanced melting of ice shelves, "the floating extensions of the ice sheet, has reduced their buttressing and caused upstream glaciers to accelerate their flow" toward the Southern Ocean. Ice shelf melting could "cause irreversible retreat" of the glaciers.
Using the United Kingdom's national supercomputer, scientists ran simulations on ocean-driven melting of ice shelves in the Amundsen Sea. They simulated a historical scenario of the 20th century and four future scenarios: two involving medium and high emissions and two using the goals of the Paris agreement, which aims to keep global temperature rise this century below 2°C, with a more ambitious target of 1.5°C, relative to preindustrial levels.
"We must not stop working to reduce our dependence on fossil fuels."
The trio of British Antarctic Survey (BAS) and Northumbria University researchers found that "rapid ocean warming, at approximately triple the historical rate, is likely committed over the 21st century, with widespread increases in ice-shelf melting, including in regions crucial for ice sheet stability."
"When internal climate variability is considered, there is no significant difference between mid-range emissions scenarios and the most ambitious targets of the Paris agreement," the study states. "These results suggest that mitigation of greenhouse gases now has limited power to prevent ocean warming that could lead to the collapse of the West Antarctic Ice Sheet."
In other words, "it looks like we've lost control of melting of the West Antarctic Ice Sheet," said lead author and BAS researcher Kaitlin Naughten in a statement. "If we wanted to preserve it in its historical state, we would have needed action on climate change decades ago."
"The bright side is that by recognizing this situation in advance, the world will have more time to adapt to the sea-level rise that's coming," Naughten noted. "If you need to abandon or substantially re-engineer a coastal region, having 50 years lead time is going to make all the difference."
"We must not stop working to reduce our dependence on fossil fuels," she stressed. "What we do now will help to slow the rate of sea-level rise in the long term. The slower the sea-level changes, the easier it will be for governments and society to adapt to, even if it can't be stopped."
As Reutersreported Monday:
The collapse of the West Antarctic Ice Sheet is one of nine global climate "tipping points" scientists identified in 2009. The passing of these environmental red lines would be catastrophic for life on Earth.
An international team of scientists said in 2022 we may already have passed the point of no return for the West Antarctic Ice Sheet at just 1.1°C of warming above preindustrial levels.
Tiago Segabinazzi Dotto, a senior research scientist at the U.K.'s National Oceanography Center who was not involved in the study, said in a statement that "it is likely that we passed a tipping point to avoid the instability of the West Antarctic Ice Sheet."
"This work fits with existing evidence that suggests that the collapse of ice shelves in the Amundsen Sea is imminent, such as the Thwaites Ice Shelf," he continued. "However, the pace of this collapse is still uncertain—it can happen in decades for some specific ice shelves or centuries."
"The conclusions of the work are based on a single model and need to be treated carefully since different models and even ensembles of the same model can give different responses," he added, while also emphasizing that "this study needs to be taken in consideration for policymakers."
Other experts who were not involved with the research also regarded its revelations as significant and echoed Naughten's call for ramping up worldwide efforts tackle the climate emergency by cutting emissions.
"This is a sobering piece of research," said University of Southampton physical oceanography professor Alberto Naveira Garabato. "It should also serve as a wake-up call. We can still save the rest of the Antarctic Ice Sheet, containing about 10 times as many meters of sea level rise, if we learn from our past inaction and start reducing greenhouse gas emissions now."
Alessandro Silvano, an independent research fellow at the Natural Environment Research Council (NERC), said that "particularly important will be the future of East Antarctica, where about 90% of the Antarctic ice is stored."
Andrew Shepherd, head of Northumbria's Department of Geography and Environment and director of the NERC Center for Polar Observation and Modeling, said that while the "conclusion about the inevitability of West Antarctic Ice Sheet collapse is pessimistic, sticking to 1.5°C of global warming buys us 50 years on the extreme scenario... and even 20 years on sticking to 2°C."
"This could make all the difference to coastal planners, and so is not to be sniffed at," he added. "It's vitally important that these ocean forcing trajectories are translated into projections of ice sheet losses so that we know what sea-level rise to expect."
The research comes as the international community prepares for COP28, the next major United Nations climate summit, set to be hosted by the United Arab Emirates in Dubai beginning next month.
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